Mine hoppers for underground use are well known. The most commonly used rail hoppers which are used to carry broken rock and reef in mines are of the bottom discharge type which include a rock container body which has an open bottom which is closed when the vehicle is loaded by one or more generally clam shaped doors. Other hopper types exist which have container body floors which are sloped to one side of the hopper and a body wall enclosure portion which is located on the floor and which at an ore pass tip is lifted with one edge of the floor or from the floor to side discharge material in the body from between the floor and the lower edge of the side wall portion of the container body.
Yet further hopper types have the floor of the container body pivotally connected at one end to the lower portion of an end wall of the body so that the body floor drops away for tipping from the opposite end wall at a tip while the wheels at that end of the hopper are supported by some lifting arrangement. In a similar hopper version the body is in one way or another tipped about a pivot arrangement on the hoper chassis to discharge material carried by the hopper through a door in one of its ends.
A problem common to hoppers of the above type which have low level doors is that broken rock and reef is loaded into the hoppers together with a fair amount of water and sludge which carries mineral fines. The sludge gravitates through rock in the hopper bodies to leak from between the doors and side walls of the hopper container bodies and into the rail ballast between the hopper rails at the hopper loading site and as the hoppers are pulled to a tip. Even though some hopper doors carry seals these become ineffective after only a small amount of use.
Not only is it a highly labor intensive, tedious and therefore expensive business continually to clean the sludge from the environs, but also a significant amount of mineral fines which are carried by the sludge is washed to waste or remains forever trapped in the rail ballast. This is a particularly serious problem in gold mining.
Yet a further problem with all known discharge rail hoppers which are discharged while they are being drawn over a tip for bottom discharge or by lifting, is that they are discharged by a tipping action in a direction transverse to the direction of hopper travel through the tip. The tipping loads thus imposed on the hoppers in this manner are high with a number of hopper types including stops or rollers which engage and run along fixed structure during tipping to prevent the hoppers from being tipped from the rails which carry them. The high tipping forces imposed on these hoppers during tipping generate higher than necessary draw loads on the locomotive pulling the hopper train throuh the tip.
Another mining problem that arises with the use of automatic discharge hoppers which are bottom discharged or tipped while moving, is that the tip excavation at the mouths to the ore passes are of necessity large and in the region of 9 to 12 meters in length making them difficult and expensive to construct while also creating large hazardous footwall areas.
Still a further problem with all tipping rail vehicles known to the applicant is the obvious loss of carrying capacity and so mine production where the vehicles are run on an incline. This is frequently a problem in mining operations in which the inclines on which the hoppers or rail vehicle skips operate are as much as 25.degree. to the horizontal.